1. Field of the Invention
This invention pertains to stripping insulation from insulated electrical conductors, and more particularly to apparatus for accurately positioning insulation cut-off and stripping blades for optimal stripping performance.
2. Description of the Prior Art
Machines for cutting and stripping insulation from insulated electrical conductors are well known, as are the cutoff and stripping blades used in the machines. For example, U.S. Pat. No. 4,577,405, the disclosure of which is incorporated herein by reference, describes compound angle blades for stripping electrical conductors. My U.S. Pat. No. 4,784,024 describes tooling for holding cut-off and stripping blades in an appropriate machine.
Referring to FIGS. 1 and 2, a pair of prior stripping blades 1 and 3 are illustrated that have generally V-shaped openings 5 and 7, respectively. Cutting edges with radii 9 and 11 are machined into the interior ends of each V-shaped opening 5 and 7, respectively. When the blades 1 and 3 are placed in facing relationship as shown in FIG. 1 and brought together in bypassing fashion, the cutting edges 9 and 11 cooperate to form a nearly round hole. When closed over an insulated conductor 13, the blades cut the insulation 15 thereon without damaging the conductor 17.
As discussed in U.S. Pat. No. 4,577,405, the V-type cutting blades 1 and 3 can strip a number of sizes of insulated electrical conductor 13 by varying the size of the hole formed by the mating blade cutting edges 9 and 11. Hole size variation is a result of the bypassing nature of the blades. The hole size is controlled by the relative positions of the blades at the end of the closing stroke. It is important to note that there is only one relative position of the cutting blades at which the cutting hole is optimally round. Turning to FIGS. 3a-3c, closing the blades down to the position shown in FIG. 3a, or opening the blades up to the position of FIG. 3c, from the optimal round hole of FIG. 3b results in an increasingly less circular hole 19.
Since there is a single position of the blades 1 and 3 that form an optimally round hole 19, it is desirable to pre-set the blades in the cutting machine such that the optimal hole is automatically formed at the end of the closing stroke. If necessary, minor final adjustments can be made after a sample insulated electrical conductor 13 is stripped. A visual inspection of the stripped insulated electrical conductor will indicate whether the blade hole must be slightly opened up or closed down from the initial setting.
Looking at FIGS. 4 and 5, a typical stripping and cutting station 21 of an insulated conductor processing machine is illustrated. The cutting and stripping station 21 includes a conventional machine frame schematically illustrated at 23. Mounted on the frame 23 for relative transverse reciprocation in the directions of arrow 25 is a front tool holder 27 and an independent rear tool holder 29. Each tool holder 27 and 29 includes a pair of longitudinally spaced apart upstanding shoulders 31 and 33, respectively. The shoulders 31 and 33 are threaded to receive set screws 35 or similar fasteners. Mounted between the respective inside faces 37 of the shoulders are a series of spacers and blades. The front tool holder carries spacers 39 together with prior stripping blades 41 and 43 and a cut-off blade 45. In applications that call for only one end of an insulated conductor piece 13 to be stripped of insulation 15, only one stripping blade, 41 or 43, is employed.
The rear tool holder 29 carries spacers 47 together with stripping blades 49 and 51 and a cut-off blade 53. The pairs of stripping blades 41, 49 and 43, 51 are located with respect to each other such that as the front and rear tool holders 27 and 29, respectively, reciprocate transversely in the directions of arrow 25, the stripping blades close over and slice the insulation of the insulated electrical conductor 13, which lies perpendicular to the direction of blade motion. Simultaneously, the cut-off blades 45 and 53 cooperate to sever the insulated conductor along line 55. Subsequent longitudinal motion of the closed stripping blades relative to the fixed insulated conductor pulls the cut lengths of insulation from the inner conductor.
In the set-up of FIGS. 4 and 5, there is no marking, reference, or indication that would aid the machine operator to pre-set the prior blades 43, 51 and 41, 49 at the desired optimum position for cutting the insulation or to make subsequent minor adjustments to the pre-set position. In most cutting and stripping machines commonly used in the industry, it is virtually impossible to view the blade hole 19 from a perspective such as is shown in FIGS. 3 and 5. Therefore, the machine operator has no idea what the actual hole size will be when he installs the tool holder/blade assemblies into the machine tooling station 21. Accordingly, it is highly desirable that an alignment reference of some type be incorporated into the cut-off and stripping blades.
To be useful, any alignment reference must meet several important functional criteria. The alignment reference must be very accurately located on the blades. Many stripping applications require stripping insulation 15 having a wall thickness of only about 0.01 inches. Therefore, the location of the alignment reference must be within a few thousandths of an inch of the desired nominal location. The thickness and edge definition of the alignment reference are also critical, since accuracy to within a few thousandths of an inch is required.
The alignment reference must be consistently located on the various cut-off and stripping blades. As shown in FIG. 4, six blades are used in a typical set up (four stripping blades 41, 43, 49, and 51 and two cut-off blades 45 and 53). The blades are manufactured, shipped, and selected at random for use in machine set ups. Accordingly, to be useful, any alignment references must be precisely located.
The alignment reference must also be a permanent part of the blades. Blades are handled many times between manufacture and use in a cutting and stripping machine. Further, the blades are used in rather harsh environments. The action of lubricants and other chemicals must be considered in connection with the type of alignment reference applied to the blades.
The alignment reference must lend itself to be easily and inexpensively applied on a production basis. Cut-off and stripping blades are perishable tools, and they are used in highly cost sensitive markets. A difference of only a few cents per blade will often determine industry acceptance of the blades.
It is conceivable that alignment marks might be placed on the longitudinal edges of the blades 41, 43, 49, and 51, since the longitudinal edges of the installed blades are normally viewable by the operator. However, scribing or etching reference lines is not only difficult to accomplish, but also such lines do not meet several of the criteria mentioned previously. For example, simply scribing a thin line on the blade would require a tolerance of the line width, narrow as it might be. The clarity of both edges of the line would have to be very distinct.
Thus, a need exists for means that facilitate the installation and set up of cut-off and stripping blades on insulated electrical conductor processing machines.